Fluorine is an essential trace element and one of the components of the human body, which, like other minerals in food, can play a role in preventing diseases. Fluorine has a role in promoting the normal development and mineralization of bones, especially for teeth, the right amount of fluorine can maintain the health of teeth and resist the sensitivity to caries. Among the various caries prevention measures currently available, the application of fluoride is an important one. Studies over the decades have shown that fluoride can reduce caries in children and adults, and can also restore early decayed teeth to normal before cavity formation. In some developed countries, fluoride has been added to drinking water since 1970s, and after years of observation, the number of children suffering from caries in these countries has been significantly reduced. Therefore, the discovery of fluoride caries prevention is regarded as one of the greatest contributions of preventive dentistry to mankind in the 20th century. Fluoride anti-caries mechanism ① When fluoride is present in plaque and saliva, it can promote remineralization of early enamel lesions; ② Fluoride interferes with glycogenolysis, and through this process, it prevents acids produced by cariogenic bacteria from metabolizing sugar; ③ Higher concentrations of fluoride have the effect of killing cariogenic bacteria and other bacteria; ④ Recent studies suggest that the intake of fluoride during tooth development makes the enamel more resistant to subsequent acid erosion. The application of fluoride is divided into two major categories: one is systemic application; the other is local application. Local fluoride is further divided into home use and professional use according to the way it is used. The former includes fluoride toothpaste, fluoride mouthwash, fluoride dental floss, fluoride toothpicks, etc.; the latter includes fluoride protective varnish, fluoride foam, etc. Compared with foreign countries, China has carried out fluoride application for a short period of time and a small scope, except for the application of fluoride toothpaste more widely, other methods of fluoride use are less. Now we introduce several simple and safe methods to prevent caries in life: 1.Brush teeth with fluoride toothpaste: twice a day, three minutes each time, at least six times for each tooth surface, so that the toothpaste can thoroughly contact with the tooth surface and let the fluoride ions in the toothpaste combine with the calcium ions in the teeth to form calcium fluoride, which plays the role of protecting teeth. 2, fluoride mouthwash: generally used mouthwash has two concentrations, namely 0.2% sodium fluoride mouthwash (used once a week) and 0.05% sodium fluoride mouthwash (used once a day), the concentration of the two mouthwashes are different, but the method of use is the same. That is, each use with 10 ml of mouthwash in the mouth, and then drum two cheeks gargle for a minute and then spit out, 30 minutes without rinsing and eating. Because rinsing and eating will dilute the content of fluorine ion in the mouth and reduce its anti-caries effect. 3.Fluorine tablet: It is suitable for children from infants to 12 years old, because the dose of fluorine tablet is different for each age, so it must be prescribed by pediatrician or dentist before taking. When taking fluoride tablets orally, it is better to chew the tablets first or swallow them after containing them, which can increase the effect. 4.Oral drops: It can be directly put into the mouth or in the vitamin preparation every day, and also can be added in the food such as cow’s milk to take quantitatively. 5.Anti-caries gel: Under the guidance of doctor, choose the plastic tray which is suitable for your oral condition. When using, open the tray first, then squeeze a gel evenly into the grooves of the upper and lower part of the tray, fold it back and put it into the mouth, let the upper and lower teeth bite in the grooves of the tray for four minutes and then take it out, and do not rinse the mouth or eat within half an hour. The anti-caries gel changed the tediousness of the above methods, it is used quarterly in the first year of use, and used once every six months from the second year onwards, it can play a good anti-caries effect. In 1995, the National Dental Control Steering Group put forward the slogan of using fluoride in appropriate amount to prevent dental caries, so using fluoride is one of the effective methods to prevent dental caries.